1. Field of the Inventions
The present disclosure relates to catalysts, for example, where noble metals can be carried in pores of a porous alumina, and a manufacturing method thereof.
2. Description of the Related Art
Emissions, such as hydrocarbon (HC) compounds, carbon monoxide (CO), and nitrogen oxides (NOx), can be discharged from internal combustion engines of automobiles as exhaust gas. Methods for removing emissions contained in the exhaust gas can use an exhaust gas purifying catalyst as well as optimization of combustion conditions, such as air-fuel ratio in the engines, in order to reduce the amount of emissions in the exhaust gas.
A so-called “three way catalyst” has been used in which noble metals such as platinum (Pt), rhodium (Rh), and palladium (Pd) are carried on a carrier of porous metal oxides, such as alumina. For example, as disclosed in Japanese Application No. JP 07-299360 A, the three way catalyst oxidates CO and HC and reduces NOx to N2. The three way catalyst acts as a catalyst at near the theoretical air-fuel ratio.
However, there are significant problems in using the catalysts of the prior art noted above. For example, exhaust gas of small, two stroke-cycle engines is so rich in unburned HC that it may be impossible to have sufficient exhaust gas purifying performance merely by diverting catalysts for four stroke-cycle engines to those for two stroke-cycle engines. In addition, since the exhaust gas of two stroke-cycle engines has extremely high temperatures, catalysts having high heat resistance are required. Thus, it is extremely difficult to have a catalyst suited for characteristics of various kinds of engines.